Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-07-11T12:39:13Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertação Mestrado M276 - Gilberto.pdf: 3559945 bytes, checksum: e0e92cec09c72c5a7b8b98260c3b9a8e (MD5) / Made available in DSpace on 2017-07-11T12:39:13Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertação Mestrado M276 - Gilberto.pdf: 3559945 bytes, checksum: e0e92cec09c72c5a7b8b98260c3b9a8e (MD5) Previous issue date: 2016-03-22 / Este trabalho apresenta um estudo comparativo de conversores monofásicos aplicados a sistemas fotovoltaicos sem transformador. Topologias de inversores sem transformador têm menores custos, tamanho e peso. Contudo, a não utilização do transformador pode ser responsável por consideráveis valores de correntes de fuga. A associação em série de vários módulos fotovoltaicos se faz necessária para alcançar o nível de tensão desejado no barramento c.c.. Com o intuito de reduzir o número de módulos fotovoltaicos em série, topologias com característica de elevação de tensão (boost) podem ser utilizadas. Portanto, topologias que possuem estas características e que possam apresentar baixos valores de correntes de fuga devem ser escolhidas para o estudo. As topologias presentes neste trabalho são: o conversor de dois estágios, o inversor fonte Z monofásico com diodo adicional, e o inversor fonte Z de três estados. / This work presents a comparative study of single-phase converters applied to transformerless photovoltaic systems. Topologies of transformerless inverters have lower costs, size and weight. However, not using it may cause considerable amounts of leakage currents. The association in series of several PV modules is needed to achieve the voltage level desired in d.c. bus. In order to reduce the number of photovoltaic modules in series, topologies with voltage boost characteristic can be used. Therefore, topologies that have voltage boost characteristic and can have low leakage current values are chosen for the study. Topologies present in this work are: the two stages single-phase converter, the single-phase Z-source inverter with additional diode, and the single-phase three switch three state Z-source inverter.

Os motores de indução desempenham um importante papel na indústria, fato este que destaca a importância do correto diagnóstico e classificação de falhas ainda em fase inicial de sua evolução, possibilitando aumento na produtividade e, principalmente, eliminando graves danos aos processos e às máquinas. Assim, a proposta desta tese consiste em apresentar um multiclassificador inteligente para o diagnóstico de motor sem defeitos, falhas de curto-circuito nos enrolamentos do estator, falhas de rotor e falhas de rolamentos em motores de indução trifásicos acionados por diferentes modelos de inversores de frequência por meio da análise das amplitudes dos sinais de corrente de estator no domínio do tempo. Para avaliar a precisão de classificação frente aos diversos níveis de severidade das falhas, foram comparados os desempenhos de quatro técnicas distintas de aprendizado de máquina; a saber: (i) Rede Fuzzy Artmap, (ii) Rede Perceptron Multicamadas, (iii) Máquina de Vetores de Suporte e (iv) k-Vizinhos-Próximos. Resultados experimentais obtidos a partir de 13.574 ensaios experimentais são apresentados para validar o estudo considerando uma ampla faixa de frequências de operação, bem como regimes de conjugado de carga em 5 motores diferentes. / Induction motors play an important role in the industry, a fact that highlights the importance of correct diagnosis and classification of faults on these machines still in early stages of their evolution, allowing increase in productivity and mainly, eliminating major damage to the processes and machines. Thus, the purpose of this thesis is to present an intelligent multi-classifier for the diagnoses of healthy motor, short-circuit faults in the stator windings, rotor broken bars and bearing faults in induction motors operating with different models of frequency inverters by analyzing the amplitude of the stator current signal in the time domain. To assess the classification accuracy across the various levels of faults severity, the performances of four different learning machine techniques were compared; namely: (i) Fuzzy ARTMAP network, (ii) Multilayer Perceptron Network, (iii) Support Vector Machine and (iv) k-Nearest-Neighbor. Experimental results obtained from 13.574 experimental tests are presented to validate the study considering a wide range of operating frequencies and also load conditions using 5 different motors.

Controlling the dynamic outputs of electrical machines has always been an essential topic in aerospace, automotive and other industries. Electrical machine control consists of several components, each of which can be controlled in various ways. Whereas the dynamic responses are mostly simulated using MATLAB/SIMULINK, Prof. Marko Hinkkanen from Aalto University has launched a project for the development of an open-source simulator called ’Motulator’, based on Python. In this thesis, we focus on developing modulation methods and related functions for the inverter in ’Motulator’ based on an existing model of a Permanent Magnet Electrical Machine (PMSM). First, the two-level and three-level inverters with the Space Vector Modulation (SVPWM) method are developed. The dynamic output performance improves significantly compared to Sinusoidal Pulse-Width Modulation (SPWM). In addition, operation under the over-modulation mode for both inverters is implemented to improve the DC-bus voltage utilisation further, allowing higher torques and speeds. The problem of neutral point voltage imbalance is solved for the three-level inverter, ensuring the difference voltage between upper and lower capacitors to fluctuate around 0. Finally, a harmonic analysis tool based on the non-uniform Fourier transform is established. / Styrning och reglering av elektriska maskiners dynamik har alltid varit ett viktigt ämne inom flyg- och bilindustrin men även för andra tillämpningar. Regleringen av elektriska maskiner består av flera delar som var och en kan styras på olika sätt. De dynamiska förhållandena simuleras vanligen i MATLAB/SIMULINK. För att inte vara beroende av kommersiell programvara har Professor Marko Hinkkanen från Aalto universitetet lanserat en simulator med öppen källkod, baserad på Python, kallad ’Motulator’. Examensarbetet fokuserar vi på att utveckla moduleringsmetoder och relaterade funktioner för växelriktaren i ’Motulator’, baserat på en befintlig modell av en permanentmagnetiserad synkronmaskin (PMSM). Först utvecklas två- och trenivåomriktare med ”Space Vector Modulation” (SVPWM). Drivsystemets dynamisk prestanda förbättras därvid avsevärt i jämförelse med Sinus-pulsbreddsstryning (Sinusoidal-PWM). Övermodulering har implementerats för båda växelriktarna i avseende att ytterligare förbättra DC-bussens spänningsutnyttjande, vilket möjliggör högre vridmoment och varvtal. Problemet med nollpunktsspänningens obalans är löst för trenivåomriktaren, vilket säkerställer att skillnadsspänningen mellan de övre och nedre kondensatorerna fluktuerar runt 0. Slutligen har ett verktyg utvecklats i syfte att analysera övertoner, baserat på en olikformig Fouriertransform.

Organic electrochemical transistors (OECTs) based on Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) are a benchmark system in organic bioelectronics. In particular, the superior mechanical properties and the ionic-electronic transduction yield excellent potential for the field of implantable or wearable sensing technology. However, depletion-mode operation PEDOT:PSS-based OECTs cause high static power dissipation in electronic circuits, limiting their application in electronic systems. Hence, having control over the threshold voltage is of utmost technological importance. Here, PEDOT:PSS-based dual-gate OECTs with solid-state electrolyte where the threshold voltage is seamlessly adjustable during operation are demonstrated. It is shown that the degree of threshold voltage tuning linearly depends on the gate capacitance, which is a straightforward approach for circuit designers to adjust the threshold voltage only by the device dimensions. The PEDOT:PSS-based dual-gate OECTs show excellent device performance and can be pushed to accumulation-mode operation, resulting in a simplified and relaxed design of complementary inverters.

This project is made for a deeper understanding ofhow frequency and amplitude of the waves that create the controlwave in a Pulse Width Modulated 2-level inverter affect the powerquality and power losses. The results were that a high frequencyreduces the Total Harmonic Distortion but increases the powerloss. The amplitude, however, reduces both the Total HarmonicDistortion and the power loss as it increases. All the analyseswere done in a simulation program called Simulink. The resultscan be applied when improving High Voltage Direct Currentinverters to develop a functional High Voltage Direct Currentgrid that enables wider use of renewable energy sources. / Projektet syftar till att få en djupare förståelse för hur frekvensen och amplituden på de vågor som skapar kontollvågen i en pulsbreddsmodulerad likspänningsomvandlare med två nivåer påverkar effektkvalitén och effektförlusterna. Resultatet av studien var att en hög frekvens minskar ”Total Harmonic Distortion” men ökar effektförlusterna. Amplituden å andra sidan reducerar både ”Total Harmonic Distortion” och effektförlusterna när den ökar. Alla analyserna är gjorda i simuleringsprogrammet Simulink. Resultaten kan appliceras när högspända likspänningsomvandlare vidareutvecklas för att skapa ett fungerande högspänt-likströms elnät som öppnar upp för en bredare användning av förnyelsebara energikällor. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm

In high power induction motor drives, the switching frequency of the inverter is quite low due to the high losses in the power devices. Real-time PWM strategies, which result in reduced harmonic distortion under low switching frequencies and have maximum possible DC bus utilisation, are developed for such drives in the present work. The space vector approach is taken up for the generation of synchronised PWM waveforms with 3-Phase Symmetry, Half Wave Symmetry and Quarter Wave Symmetry, required for high-power drives. Rules for synchronisation and the waveform symmetries are brought out. These rules are applied to the conventional and modified forms of space vector modulation, leading to the synchronised conventional space vector strategy and the Basic Bus Clamping Strategy-I, respectively. Further, four new synchronised, bus-clamping PWM strategies, namely Asymmetric Zero-Changing Strategy, Boundary Sampling Strategy-I, Basic Bus Clamping Strategy-II and Boundary Sampling Strategy-II, are proposed. These strategies exploit the flexibilities offered by the space vector approach like double-switching of a phase within a subcycle, clamping of two phases within a subcycle etc. It is shown that the PWM waveforms generated by these strategies cannot be generated by comparing suitable 3-phase modulating waves with a triangular carrier wave. A modified two-zone approach to overmodulation is proposed. This is applied to the six synchronised PWM strategies, dealt with in the present work, to extend the operation of these strategies upto the six-step mode. Linearity is ensured between the magnitude of the reference and the fundamental voltage generated in the whole range of modulation upto the six-step mode. This is verified experimentally. A suitable combination of these strategies leads to a significant reduction in the harmonic distortion of the drive at medium and high speed ranges over the conventional space vector strategy. This reduction in harmonic distortion is demonstrated, theoretically as well as experimentally, on a constant V/F drive of base frequency 50Hz for three values of maximum switching frequency of the inverter, namely 450Hz, 350Hz and 250Hz. Based on the notion of stator flux ripple, analytical closed-form expressions are derived for the harmonic distortion due to the different PWM strategies. The values of harmonic distortion, computed based on these analytical expressions, compare well with those calculated based on Fourier analysis and those measured experimentally.

This thesis deals with modeling, simulation and implementation of Load Commutated SCR based current source Inverter (LCI) fed squirrel cage induction motor drive with sinusoidal voltage and sinusoidal current. In the proposed system, the induction motor is fed by an LCI. A three level diode clamped voltage source inverter (VSI) is connected at the motor terminal with ac chokes connected in series with it. The VSI currents are controlled in such a manner that it injects the reactive current demanded by the induction motor and the LCI for successful commutation of the SCRs in the LCI. Additionally, it absorbs the harmonic frequency currents to ensure that the induction motor draws sinusoidal current. As a result, the nature of the motor terminal voltage is also sinusoidal. The concept of load commutation of the SCRs in the LCI feeding an induction motor load is explained with necessary waveforms and phasor diagrams. The necessity of reactive compensation by the active filter connected at the motor terminal for the load commutation of the thyristors, is elaborated with the help of analytical equations and phasor diagrams. The requirement of harmonic compensation by the same active filter to achieve sinusoidal motor current and motor voltage, is also described. Finally, to achieve the aforementioned induction motor drive, the VA ratings of the active filter (VSI) and the CSI with respect to VA rating of the motor, are determined theoretically. The proposed drive scheme is simulated under idealized condition. Simulation results show good steady state and dynamic response of the drive system. Load commutation of the SCRs in the LCI and the sinusoidal profile of motor current and voltage, have been demonstrated. As in LCI fed synchronous motor drives, a special mode of operation is required to run up the induction motor from standstill. As the SCRs of the LCI are load commutated, they need motor terminal voltages for commutation. At standstill these voltages are zero. So, a starting strategy has been proposed and adopted to start the motor with the aid of the current controlled VSI to accelerate until the motor terminal voltages are high enough for the commutation of the SCRs in the LCI. The proposed drive is implemented on an experimental setup in the laboratory. The IGBT based three level diode clamped VSI has been fabricated following the design of the standard module in the laboratory. A generalized digital control platform is also developed using a TMS320F2407A DSP. Two, three phase thyristor bridges with necessary firing pulse circuits have been used as the phase controlled rectifier and the LCI respectively. Appropriate protection scheme for such a drive is developed and adopted to operate the drive. Relevant experimental results are presented. They are observed to be in good agreement with the simulation results. The effect of capacitors connected at the output of the LCI in the commutation process of the SCRs in the LCI is studied and analyzed. From the analysis, it is understood that the capacitors form a parallel resonating pair with filter inductor and the motor leakage inductance, which results in an undesired oscillation in the terminal voltage during each of the commutation intervals leading to commutation failure. So, in the final system, the capacitors are removed to eliminate any chance of commutation failure of the SCRs in the LCI. It is shown by experiment that the commutation of the SCRs takes place reliably in the absence of the capacitors also. The commutation process is studied and analyzed without the capacitors to understand the motor terminal voltage waveform of the experimental results.

Η παρούσα διδακτορική διατριβή εστιάζεται στον χώρο των Φ/Β πλαισίων εναλλασσομένου ρεύματος (AC-PV Modules) με μετατροπείς δύο βαθμίδων, και πιο συγκεκριμένα σε μετατροπείς Σ.Τ. – Σ.Τ με τους οποίους επιτυγχάνεται ανύψωση της τάσης και μπορούν να αποτελέσουν την πρώτη από τις δύο βαθμίδες. Τρεις είναι οι κύριοι στόχοι: A)Η εύρεση της καταλληλότερης επιλογής για την πρώτη βαθμίδα της διάταξης σύνδεσης ενός Φ/Β πλαισίου στο μονοφασικό δίκτυο χαμηλής τάσης. B)Ο βέλτιστος σχεδιασμός και η επιλογή του κατάλληλου Πολλαπλασιαστή Τάσης. C)Ο βέλτιστος σχεδιασμός της μονάδας ανύψωσης τάσης, η οποία αποτελεί την πρώτη βαθμίδα, μιας διάταξης δύο βαθμίδων, για τη σύνδεση Φ/Β πλαισίου με το δίκτυο χαμηλής τάσης. Η μελέτη των τυπικών επιπέδων τάσης που εμφανίζονται σε διατάξεις διασύνδεσης δύο βαθμίδων απέδειξε την ανάγκη σχεδιασμού μετατροπέων Σ.Τ.-Σ.Τ. με υψηλά κέρδη τάσης, τα οποία δεν μπορούν να προσφέρουν οι κλασσικοί μετατροπείς. Το γεγονός αυτό αποτέλεσε το έναυσμα για τη διερεύνηση της λειτουργικής συμπεριφοράς των Πολλαπλασιαστών Τάσης και εστιάσθηκε στην εξαγωγή νέων απλών και ακριβέστερων μαθηματικών σχέσεων για τη λειτουργία τους, στον ορισμό και την υλοποίηση του βέλτιστου σχεδιασμού και τέλος στη βέλτιστη επιλογή των στοιχείων του κυκλώματος. Για τον καλύτερο δυνατό σχεδιασμό του ανυψωτή τάσης διεξάγεται τεκμηριωμένη σύγκριση μεταξύ διαφόρων δημοφιλών τοπολογιών Πολλαπλασιαστών Τάσης, καθώς και της μορφής της τάσης που θα τον τροφοδοτεί. Η εκτεταμένη έρευνα καταλήγει στην εφαρμογή θετικής παλμικής τάσης εισόδου, με τη χρήση μιας παραλλαγής του μετατροπέα Boost (Mod Boost), ενώ επικρατέστερος Πολλαπλασιαστής Τάσης είναι μία παραλλαγή του Half-Wave Cockcroft-Walton με πυκνωτή εξομάλυνσης (Modified Half-Wave Cockcroft-Walton with Smoothing Capacitor). Στα πλαίσια της διδακτορικής διατριβής προτείνεται επιπλέον ένας νέος επαναληπτικός αλγόριθμος, ο οποίος συνδυάζει επιτυχώς θεωρητικές εξισώσεις και προσομοίωση, έχοντας ως στόχο το βέλτιστο σχεδιασμό του σύνθετου ανυψωτή τάσης, ο οποίος ονομάστηκε “Mod Boost – Mod H-W C-W SC VM” και συνίσταται από τον τροποποιημένο μετατροπέα Boost και τον προαναφερθέντα Πολλαπλασιαστή Τάσης. Τα συμπεράσματα και τα θεωρητικά αποτελέσματα της παρούσας διδακτορικής διατριβής επιβεβαιώνονται μέσω της προσομοίωσης και της σύγκρισης με κατάλληλα εργαστηριακά πρωτότυπα. / The current PhD thesis focuses on the field of AC PV Modules using Dual-Steps Inverters and more specifically on DC-DC Converters that are voltage boosters and can act as the first one of the two stages of the inverter. Three goals are accomplished in this work: A)The optimum choice of the topology for the first stage of a dual steps inverter of an AC-PV Module connected to the single-phase low voltage utility grid. B)The optimum choice and design of the Voltage Multiplier. C)The optimum design of the first stage of a dual steps inverter of an AC-PV Module. The analysis of the typical voltage levels at the dual steps topologies turns the research interest to DC-DC Converters with voltage gain (more than 20) higher than what is typical for the classical topologies. Based on that, a theoretical analysis is held on Voltage Multipliers according to which the crucial magnitudes are highlighted and new, simple and accurate formulas are extracted, which describe the operation of the voltage multipliers. Moreover theoretical supported choices about the capacitances in every stage are suggested, an optimum design is determined and for its implementation new accurate easy-to-use formulas are extracted. For an optimal design of the voltage booster, well established comparisons are made between popular types of voltage Multipliers and voltage triggering sources. The intensive research leads to the use of a positive voltage pulsing source that is generated by a modified Boost converter (Mod Boost Converter). Moreover a modified Half-Wave Cockcroft-Walton with Smoothing Capacitor VM is set as the best choice among the studied Voltage Multipliers. Furthermore, a novel iterative optimum design algorithm is introduced, which uses both the theoretical equations of a VM optimum design and a simulation software, so as to make feasible an optimum design of the novel DC-DC Converter. The new converter, named Mod Boost – Mod H-W C-W SC VM, results from the series connection of the modified converters Boost and Half Wave Cockcroft Walton with Smoothing Capacitor VM. Finally, the conclusions and the theoretical analysis of this work are validated by PSPICE simulations and experimental results, extracted by measurements on laboratory prototypes.

Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη ενός συστήματος διασύνδεσης μιας ανεμογεννήτριας ονομαστικής ισχύος 1kW με το δίκτυο χαμηλής τάσης. Επιπλέον, πραγματεύεται τη σχεδίαση, κατασκευή και έλεγχο ενός τριφασικού αντιστροφέα που αποτελεί την τελευταία βαθμίδα πριν τη σύνδεση με το δίκτυο χαμηλής τάσης. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Σκοπός είναι η διασύνδεση της ανεμογεννήτριας με το δίκτυο χαμηλής τάσης μέσω δύο βαθμίδων: ενός μετατροπέα ανύψωσης τάσης και ενός τριφασικού αντιστροφέα. Ο μετατροπέας ανύψωσης τάσης αποτελεί αντικείμενο μελέτης της διπλωματικής εργασίας του συνάδελφου Ιωάννη Γκαρτζώνη, ενώ στην παρούσα διπλωματική εργασία μελετάται και σχεδιάζεται ο τριφασικός αντιστροφέας. Αμφότερες οι διατάξεις περιλαμβάνουν ελέγχους κλειστού βρόχου, μέσω των οποίων απομαστεύεται η μέγιστη ισχύς από την ανεμογεννήτρια (έλεγχος μετατροπέα ανύψωσης) και διατηρείται σταθερή η τάση μεταξύ των δύο βαθμίδων, παρέχοντας ενεργό ισχύ στο δίκτυο υπό μοναδιαίο συντελεστή ισχύος (έλεγχος τριφασικού αντιστροφέα). Αρχικά παρουσιάζονται τα πλεονεκτήματα και μειονεκτήματα της χρήσης ανεμογεννητριών για την παραγωγή ηλεκτρικής ενέργειας και αναλύεται ο τρόπος με τον οποίο η αιολική ενέργεια μετατρέπεται σε ηλεκτρική. Επιπλέον, γίνεται μια σύντομη αναφορά στους τύπους των ανεμογεννητριών, καθώς και στους τρόπους λειτουργίας τους ως προς τη διασύνδεση με το δίκτυο. Στη συνέχεια γίνεται θεωρητική ανάλυση για κάθε βαθμίδα του συνολικού συστήματος. Ιδιαίτερη έμφαση δίνεται στη λειτουργία του τριφασικού αντιστροφέα και στην τεχνική παλμοδότησής του που ονομάζεται Ημιτονοειδής Διαμόρφωση του Εύρους των Παλμών (Sinusoidal Pulse Width Modulation - SPWM). Επίσης, εξάγονται σχέσεις βάσει των οποίων είναι δυνατό να παραμετροποιηθεί ο τριφασικός μετασχηματιστής με μεγάλη επαγωγή μαγνήτισης που έπεται του τριφασικού αντιστροφέα. Το επόμενο βήμα αποτελεί η προσομοίωση στο λογισμικό προσομοίωσης κυκλωμάτων Simulink του Matlab τόσο του τριφασικού αντιστροφέα σε ανοιχτό και σε κλειστό βρόχο, όσο και ολόκληρου του συστήματος διασύνδεσης. Ο κλειστός βρόχος αποτελεί ένα νέο και άμεσο έλεγχο της ισχύος που παρέχεται στο δίκτυο. Επιπρόσθετα, περιγράφεται ο σχεδιασμός και η κατασκευή όλων των κυκλωμάτων που απαιτούνται για τον τριφασικό αντιστροφέα, το φίλτρο και το μετασχηματιστή. Τέλος πραγματοποιούνται πειραματικές δοκιμές για να διαπιστωθεί η ορθή λειτουργία των βαθμίδων που κατασκευάστηκαν, να εντοπιστούν και δικαιολογηθούν τυχόν διαφορές μεταξύ της θεωρητικής ανάλυσης και των μετρήσεων στην πραγματική διάταξη, καθώς και για να εκτιμηθεί η απόδοση του συστήματος. / The present diploma thesis deals with the interconnection of 1kW wind generator to the low voltage grid. A three phase inverter is the last stage of the interconnection system. The design, construction and control of the three phase inverter is studied. This work was developed in the Laboratory of Electromechanical Conversion Energy at the Department of Electrical Engineering and Computer Technology of Polytechnic School in the University of Patras, Greece. The purpose of this thesis is the connection of the wind generator with the low voltage grid through two stages: a boost converter and a three phase inverter. Both stages are closed loop controlled and in this way the maximum power of the wind generator is supplied (control of the boost converter) and the voltage between the two stages remains constant, providing active power to the grid with unity power factor (control of the three phase inverter). Initially, the advantages and disadvantages of the use of wind generator are presented and the way that the wind energy is converted to mechanical energy and finally to electrical energy is analyzed. Moreover, it is given a short reference in the types of the wind generators used for connection to the grid. In addition, every stage of the whole system is analyzed. Especially, the function of the three phase inverter and the Sinusoidal Pulse Width Modulation-sPWM are studied. The three phase transformer, that follows the three phase inverter stage, is parameterized through equations that are described in this work. The next step in this thesis is the simulation with Simulink of Matlab. The three phase inverter is simulated in open and closed loop as well as the whole connection system of the wind generator to the low voltage grid. The closed loop control is a new and direct control of active and reactive power that are supplied to the grid. Furthermore, it is described the design and construction of all the circuits for the three phase inverter, the filter and the transformer. Finally, experiments are conducted in order to confirm the proper function of the stages that are constructed, to find differences between theory and reality and to estimate the efficiency factor of the system.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This thesis contributes to the analysis, project and implementation of discrete-time controllers based on the Internal Model Principle, aiming to improve the performance of three-leg three-phase PWM inverters with insulating output transformer usually found in the output stage of medium power double-conversion UPS. Initially, an investigation about issues concerning to the discrete-time models of three-phase inverters with space vector modulation and the LC filter have been carried out. This investigation shows the impact of different switching sequences, sampling instants and filter cut-off frequency on the harmonic spectrum of sampled variables used for feedback. This is a concern when the switching frequency is low to limit the switching losses as in medium and high power UPS. In this way, this thesis proposes sampling methods that make possible to reduce the low order harmonics on the interest variables, which is relevant when state feedback is used. These methods allow to obtain discrete-time average linear models useful for the controller design. In addition, the saturation of the insulating transformer is addressed in details. The dc component arising from the digital implementation and from the circuit measures non idealities, and then amplified by an inadequate choice of the controller, may lead the transformer to saturate. In order to solve this problem, and in accordance with the Internal Model Principle, internal models adequate to the plant under consideration as well as discrete-time voltage controllers in stationary and synchronous frames which are not prone to amplify the dc component, are proposed. Another goal of this thesis is the improvement of the UPS output voltage transient response due to linear and non linear load steps. This is obtained considering the sampling methods before mentioned, combined with internal models with reduced number of poles and low sampling rate. It is demonstrated that it is possible to improve significantly the output voltage transient responses, as well as to satisfy the rigorous classification of the standard IEC62040-3 for UPS without degrading the steady state performance. In addition, these control structures have enough stability margins, as proved in each case, and they results in simple and attractive solutions to be implemented in 8 or 16 bits fixed-point arithmetic microcontrollers and DSP with reduced memory space. The feasibility of the proposed solutions is verified with experimental results demonstrating both transient and steady-state performances. Finally, a comparative analysis of the proposed control structures, over the light of the standard IEC62040-3, is presented. / A presente tese de doutorado contribui para a análise, projeto e implementação de controladores discretos baseados no Princípio do Modelo Interno, com o intuito de aprimorar o desempenho de inversores trifásicos PWM a três braços com transformador isolador usualmente utilizados no estágio de saída de UPS de dupla conversão de média potência. Inicialmente se realiza uma investigação sobre os aspectos relacionados à obtenção do modelo discreto de inversores trifásicos com modulação space vector e do filtro de saída. Essa investigação mostra o impacto de diferentes seqüências de comutação, instantes de amostragem e freqüência de corte do filtro no conteúdo harmônico das variáveis amostradas usadas para realimentação. Isso é uma preocupação quando a freqüência de comutação é baixa para limitar as perdas em UPS de média e alta potência. Nesse sentido essa tese propõe métodos de amostragem que possibilitam reduzir as harmônicas de baixa ordem nas variáveis de interesse o que adquire importância quando se realiza a realimentação dos estados da planta. Esses métodos permitem a obtenção de modelos médios lineares úteis para o projeto do controlador. Além disso, a saturação do transformador de isolação é analisada em detalhe. A componente contínua oriunda da implementação digital e das não idealidades dos circuitos de medição, e amplificada por uma escolha inadequada do controlador, pode levar o transformador à saturação. Com o intuito de solucionar esse problema, e de acordo com a teoria do Princípio do Modelo Interno, são propostos modelos internos adequados à planta em questão bem como controladores discretos de tensão em eixos estacionários e síncronos, que não tem tendência a amplificar a componente contínua. Outro dos objetivos dessa tese é o aprimoramento da resposta transitória das tensões de saída da UPS na presença de degraus de carga linear e não linear. Isso é obtido considerando-se os métodos de amostragem mencionados acima, combinado com modelos internos com número de pólos e taxa de amostragem reduzidos. Demonstra-se que é possível aprimorar significativamente a resposta transitória das tensões de saída bem como satisfazer a exigente classificação da norma IEC62040-3 para UPS, sem degradar o desempenho de regime permanente. Além disso, essas estruturas de controle possuem suficiente margem de estabilidade, como provado em cada caso, e estas resultam em soluções simples e atrativas para serem implementadas em microcontroladores e DSP de aritmética de ponto fixo, com palavras de 8 e 16 bits e capacidade reduzida de memória. A viabilidade prática das propostas realizadas é verificada com resultados experimentais em regime permanente e transitório. Finalmente, apresenta-se uma análise comparativa das estruturas de controle propostas, sob o enfoque da norma IEC62040-3.